January 9, 2014

Clymene Dolphin May Be Rare Product Of Natural Hybridization

Natural hybridization between two dolphin species likely helped to bring about the mysterious clymene dolphin, according to a study published in the open-access journal PLOS ONE.

Researchers from several institutions found in a molecular analysis that spinner dolphins and striped dolphins helped create the clymene dolphin. Questions about the clymene dolphin’s origins have been unanswered for many years, so the team from the Wildlife Conservation Society, the American Museum of Natural History's Sackler Institute for Comparative Genomics, the University of Lisbon, and other contributing groups decided to solve this riddle once and for all.

Taxonomists originally considered the clymene dolphin a subspecies of the spinner dolphin,but in 1981, scientists began to recognize it as a distinct species. However, the latest study sought to clarify its origins, finding that it was a result of natural hybridization.

"Our study represents the first such documented instance of a marine mammal species originating through the hybridization of two other species,"stated Ana R. Amaral, lead author of the study and research associate at the American Museum of Natural History. "This also provides us with an excellent opportunity to better understand the mechanisms of evolution."

Clymene dolphins have a similar physical appearance to their relatives, and the latest genetic results show why. Natural hybridization is a fairly common process in the evolutionary history of plants, fishes and birds, but is considered rare among mammals.

Researchers examined the nuclear and mitochondrial DNA from skin samples obtained from both free-ranging dolphins by means of biopsy darts as well as dolphins obtained through stranding events. The team amplified one mitochondrial DNA marker and six nuclear DNA markers to help analyze the evolutionary relationship between the clymene dolphin and its closest relatives.

Results showed the level of discordance among the nuclear and mitochondrial markers from the three species is best explained as an instance of natural hybridization. They found that while the mitochondrial genome of the clymene dolphin resembles the striped dolphin the most, the nuclear genome has a closer relationship to the spinner dolphin.

The researchers wrote that although non-reticulate forms of evolution, in which there is no cross-mating between species, could explain the genetic results, the genetic and morphological evidence points strongly toward their speciation.

“We anticipate that our study will bring attention to this important aspect of reticulate evolution in non-model mammal species. The study of speciation through hybridization is an excellent opportunity to understand the mechanisms leading to speciation in the context of gene flow,” the authors wrote in the journal.

Clymene dolphins grow to nearly seven feet in length and inhabit the tropical and temperate zones of the Atlantic Ocean.

"Very little is known about the clymene dolphin, whose scientific name translated from Greek is oceanid, but ironically also can mean fame or notoriety. Hopefully, our work will help draw greater attention to these dolphins in large parts of their range,” stated Dr. Howard Rosenbaum, Director for WCS's Ocean Giants Program and a senior author on the study.